The alkalic gold-porphyry deposits of the Cadia district are located in the eastern Lachlan Fold belt of New South Wales, Australia. The district comprises four porphyry deposits (Ridgeway, Cadia Quarry, Cadia Hill and Cadia East – Far East) and two related skarn deposits (Big Cadia and Little Cadia).
To 2003, in excess of 700 tonnes of gold and 3 million tonnes of copper have been identified in these deposits, making Cadia the world’s largest known alkalic gold-copper porphyry district on the basis of contained gold. Two styles of porphyry deposit have been defined.
(1) ‘Intrusive-centred’, in which mineralisation is localised within and around a temporally and genetically related intrusive complex (Ridgeway, Cadia East – Far East) where both intrusion and the enclosing volcanic wallrocks host mineralisation.
(2) ‘Intrusive wall rock’ deposits, in which the mineralisation is hosted within monzonite but there is no textural evidence to support a genetic link between mineralisation and host intrusion (Cadia Quarry, Cadia Hill). The intrusive-centred deposits have a well constrained pattern of alteration and mineralisation. The intrusive wall rock deposits display subtle alteration patterns that are thought to be a result of the buffering capacity of the monzonite country rocks.
(Source: Wilson, 2003)